Structure Modification And Application Of Ionic Conductor Based On Imidazolium Salts In Solid State Dye Sensitized Solar Cells

One of the limitations to the indurstrilization of dye-sensitized solar cells (DSSCs) is the poor long-term stability. Development of solid electrolytes for all-solid-state DSSC devices is an effective way to overcome this problem. Solid ionic conductors, whcih can penetrate the TiO2 well and are easy to synthesize, are an important class of solid electrolyte. In this thesis, we designed and synthesized a series of imidazolium iodide based ionic conductors through structural modifications of the imidazolium ring and applied them as the solid electrolyte in DSSCs as detailed below:(1) We designed and synthesized a series of imidazolium salts with different functional groups as solid state electrolytes for DSSCs. Ionic conductor’s conductivity was gradually improved when the alkyl groups were replaced with an ester group and further with a hydroxyethyl group. The ester and hydroxyethyl functionalized imidazolium iodide mixed with iodine and Lil could achieve a power conversion efficiency of 7.45%. Further improvement of ionic conductivity could be realized by linking two ester groups to the imidazolium ring, which could act as a single-component solid electrolyte made the solid DSSCs work without any additives.(2) To minimize the charge recombination between electrons and the electron acceptor in solid-state dye-sensitized solar cells, we proposed to separate electron donor and acceptor in the photoanode and cathode, respectively. Owing to the absence of the acceptor in the photoanode initially, the charge recombination rate was retarded remarkably, resulting in an increase of the short-circuit photocurrent, open-circuit photovoltage and power conversion efficiency.(3) We synthesized a new ionic conductor by linking an ether group to the nitrogen atom of 1,2-dimethylimidazole with an iodide counter anion and its single crystal structure was determined by X-ray crystallographic analysis. When the solid ionic conductor was mixed with Lil and I2 as the solid electrolyte for use in solid-state DSSCs, power conversion efficiency of 7.55% has been achieved under AM1.5G one-sun illumination.(4) Double-propargyl substituted imidazolium iodide was designed and synthesized, which as a single-component solid electrolyte could operate solid DSSCs efficiently with efficiency of 6.8%. The analysis of single-crystal structure revealed that the strong π-π interaction between propargyl was favorable for high conductivity and hence high efficiency.(5) A series of ether functionalized poly ionic liquids (PILs) were synthesized for solid DSSCs. Upon introduction of ether group and the increase of the number of ether oxygen atom, the polymer’s flexibility was improved, resulting in improved conductivity and hence solar cell performance.